Rotary helically splined actuators have been employed in the past to achieve the advantage of high-torque output from a simple linear piston-and-cylinder drive arrangement. The actuators typically employed a cylindrical body with an elongated rotary output shaft extending from end to end coaxially within the body, with an end portion of the shaft providing the drive output. Disposed between the body and the shaft is a piston sleeve splined to cooperate with corresponding splines on the body interior and the output shaft exterior. The piston is reciprocally mounted within the body and has a head for the application of fluid pressure to one or the other opposing sides thereof to produce axial movement of the piston. The sleeve is elongated and coaxially receives the shaft therein.
As the piston linearly reciprocates in an axial direction within the body, the outer splines of the sleeve engage the splines of the body to cause rotation of the sleeve. The resulting linear and rotational movement of the sleeve is transmitted through the inner splines of the sleeve to the splines of the shaft to cause the shaft to rotate. Bearings are typically supplied to rotatably support one or both ends of the shaft relative to the body. With such an arrangement, the overall length of the actuator is frequently dictated by the shaft length. Furthermore, the rotary output of the actuator is transferred by connection of another device or shaft to an end of the output shaft located at one or the other ends of the body. There are situations, however, where it is desirable or mandatory to shorten the overall length of the actuator or to have the rotary output other than at the case ends.
It will therefore be appreciated that there has been a significant need for a rotary actuator with a decreased axial length and with means for connection of the rotary output of the actuator to an external device or shaft other than at the ends of the case. The present invention fulfills this need and further provides other related advantages.